Knee braces and supports are widely used to treat a variety of knee infirmities. Such braces may be configured to impart forces or leverage on the limbs surrounding the knee joint to relieve compressive forces within a portion of the knee joint or to reduce the load on that portion of the knee. If knee ligaments are weak and infirm, a knee brace may stabilize, protect, support, or rehabilitate the knee.
The knee is acknowledged as one of the weakest joints in the body and serves as the articulating joint between the thigh and calf muscle groups. The knee is held together primarily by small but powerful ligaments. Knee instability arising out of cartilage damage, ligament strain, and other causes is relatively commonplace since the knee joint is subjected to significant loads during the course of almost any kind of physical activity that requires using the legs.
A healthy knee has an even distribution of pressure in both the medial and lateral compartments of the knee. It is normal for a person with a healthy knee to place a varus moment on the knee when standing so the pressure between the medial and lateral compartments is uneven but still natural.
One type of knee infirmity that many individuals are prone to having is compartmental osteoarthritis. Compartmental osteoarthritis may arise when there is a persistent uneven distribution of pressure in one of the medial and lateral compartments of the knee. Compartmental osteoarthritis can be caused by injury, obesity, misalignment of the knee, or aging of the knee.
A major problem resulting from osteoarthritis of the knee is that the smooth cartilage lining the inside of the knee wears away. This leads to a narrowing of the joint space, and therefore the knee develops cysts and erosions in the bone ends. Because of the narrowing of the joint, bone comes directly in contact with bone, and an uneven distribution of pressure develops across the knee, which may cause the formation of bone spurs around the joint. All of these changes ultimately lead to increasing pain and stiffness of the joint.
While there are no cures to osteoarthritis, there are many treatments. Individuals who have a diagnosis of isolated medial compartmental osteoarthritis of the knee are confronted with a variety of treatment options such as medications, surgery, and nonsurgical interventions. Nonsurgical interventions include using canes, lateral shoe wedges, and knee braces.
Knee bracing is useful to provide compartment pain relief by reducing the load on the compartment through applying an opposing external valgus or varus moment about the knee joint. Unloading knee braces have been shown to significantly reduce osteoarthritis knee pain while improving knee function.
Straps used in an unloading knee brace are commonly referred to as dynamic force straps (DFS), and create unloading as the straps become taut, yet due to the mechanics of the brace, the straps only become taut when the knee is close to full extension. As shown in FIG. 1, the unloading is only achieved at low degrees of flexion. In referring to FIG. 2, during normal gait, loading of the knee only happens when flexion angles are less than 15-20 degrees.
During activities, such as walking up stairs and steep slopes, loading can occur at greater flexion angles than those required under normal walking circumstances. The knee angles during stair ascent can be seen in FIG. 3, which demonstrates that unloading should be provided for flexion at greater angles. Conventional dynamic force straps fall short of providing unloading at such greater angles.
Microfracture surgery can be an indication for unloading braces. Microfracture surgery is only indicated if the unloading type brace can provide unloading at the flexion at which the cartilage defect is part of the joint contact surface. Such unloading at the required degree of flexion is not typically obtainable with conventional dynamic force straps.